An objective lens, sometimes referred to as a diverger, may be used to transform a collimated beam into a diverging (or converging) beam. In the field of interferometry, an objective lens may be used with an interferometer to address a part under test. The objective lens transforms a collimated beam from the interferometer into a diverging (or converging) beam that fills the numerical aperture of a part under test. The part may be directly addressed, as is typical for a spherical surface, or addressed through a null lens or other apparatus.